manufacture of diffraction gr

importance that the rms roughness of the surface of the black layer coating be less than 15 Å. It would be an advantage if the coating could be applied not only to aluminum but also to other substrate mate-rials, such as Pyrex. It is desirable that the reflectance of the treated interface be of the order of 0.1 % and certainly less surfaces used on space shuttle missions for the Ca-nadian Space Agency. Coatings made of these ma-terials are space qualified. They do not age significantly, and they withstand cleaning with ace-tone and caustic soda. In addition, they can be etched without problems. A thin, adhesive layer might have to be included to enhance the adhesion of the resist to the top SiO2 layer. It is well known see, for example, Refs. 2–5 that black layer coatings based on thin-film interference consist of transparent, nonabsorbing materials and of thin, semitransparent metallic layers. The nonab-sorbing layers are relatively thick, and errors in their thicknesses primarily result in wavelength shifts of the resulting coatings. To find a solution that is less sensitive to such thickness errors calls for design specifications with a low reflectance in the 390– 450-nm spectral region, even though the reflectance needs to be low at only at 413 nm. These low